Darcy's law–based numerical simulation for modeling 3D liquid absorption into porous wicks

Abstract

Liquid imbibition into polymer wicks, where a clear liquid front can be seen rising during the wicking process, is modeled using the concepts of flow in porous media. The flow of liquid behind the moving liquid front is modeled using the physics of single-phase flow in a porous medium where the Darcy's law is combined with the continuity equation and a capillary suction pressure is imposed at the liquid front. A novel numerical simulation PORE-FLOW^© based on the finite element/control volume method is proposed to model such imbibitional flows in wicks of complex shapes. A validation of the simulation is obtained by achieving an excellent comparison of its predictions with an experimental result, an analytical solution, and the Washburn equation for the case of wicking against gravity in a cylindrical wick. The simulation is also used to predict a case of two-dimensional (2D) wicking in the altered cylindrical wicks with two different cross-sectional areas. Once again an excellent match is obtained with the experimental results, while analytical solutions for the single and double cross-section cases along with the Washburn equation fail to predict the 2D wicking. Later, some other types of altered wicks with sharp changes in their cross-sectional areas were analyzed numerically for their wicking behavior. It was observed that the height of liquid front in a vertical wick as a function of time, which is proportional to the history of liquid imbibed, is strongly dependent on the extent of reduction in the wick cross-sectional area as well as its location vis-à-vis the wick entrance. © 2010 American Institute of Chemical Engineers AIChE J, 2011